If your Google Analytics (GA) tracking code is used by someone else on another domain, their data will appear on your GA dashboard... It took me a while to figure out what was going on the first time this happened to me so here's the story and solution.

It starts with strange pages showing up in your most/recent visited page list. Pages that you know are not on your domain. When you click the little “open this URL in a popup” button, it will try to load that page on your domain, which won’t work and probably leads you to a 404. So how the hell do so many visitors seem to visit this broken URL?
My first guess was that certain of my site’s assets were being hot-linked, but that doesn’t make much sense because the GA script won’t fire unless the surrounding HTML page is viewed. Then after some googling around for similar cases, I discovered it simply means your tracking code is being abused on other domains. *Mind blow*

In my case it was directly copied from one of my plugin’s live demo pages and not removed. The trickiest part though, is that GA won’t tell you on what domain your page views occur. It just shows you the URL after the first slash, and even assumes it’s on your own domain when you ask for more details about the specific page.

TL;DR

The easy solution is to add a filter to only include your own domain’s tracking data (the crazy solution would be hunting down the domain(s) that are using your tracking code and politely asking them to remove it!).

Note that these steps apply to the GA interface of early 2013, and can vary anytime later.

1. When on a profile’s dashboard, click the Admin button
2. Click on your profile
3. Click the Filters tab
4. “New filter”
5. Under filter type; choose “Include only” – “traffic to the hostname” – “that are equal to” – “[yourdomain.ext]”

Your GA profile will stay clean starting the next day (older data remains in the analytics history).